Cathode for an electric discharge tube

ABSTRACT

A cathode suitable for poor vacuum conditions and repeated exposures to air consists of a molybdenum support, compact or compressed powder, welded on a tungsten wire and having thereon a compressed mixture of rhenium with lanthanum hexaboride. Instead of rhenium, a tungsten boride such as W2B or W2B5 may be chosen.

United States Patent 1191 Laffcrty 313/346 X van Stratum et al. 11 July 9, 1974 [5 CATHODE FOR AN ELECTRIC DISCHARGE 3,312,856 4/1967 Lafferty et al. 313/337 x 'TUBE 3,440,475 4/1969 Schiller et al...... 313/337 3,462,635 8/1969 Broers 313/337 [75] lnventorsz' Antonius Johannes Alberta van 3,532,923 10/1970 Vogel 1 313/336 X Stratum; Pieter Zalm, both of 3,631,291 12/1971 Favreau 313/336 Emmasingel Eindhoven; Niranjan Kumar Mitra, Best, all of N th l d Primary Egizminerilsamis lA!.Clawrence Assistant aminer ax 1e atmon, Jr.' [73] Asslgnee: Ph'hps corporatwn New Attorney, Agent, or Firm-Frank R. Trifari; Carl P.

, York Steinhauser [22] Filed: May 25, 1973 [2]] Appl. No.: 363,877

[57] ABSTRACT [30] Foreign Appllcation Priority Data A cathode suitable for poor vacuum conditions and May 30, I972 Netherlands ..7207276 repeated exposures to air consists of a molybdenum support, compact or compressed powder, welded on a [52] US. Cl. 313/346, 313/337 tungstan Wire and having thereon a compressed [51] Int. Cl H01] 1/14, H01] 19/06 ture of rhenium with lanthanum hexaboride. Instead [58] Field Of Search 313/336, 337, 346 of rhenium, a tungsten boride Such as WzB or W285 may be chosen. [56] References Clted UNITED STATES PATENTS 2 Chin's, 1 Drawing Figure 2,659,685 ll/l953 CATHODE FOR AN ELECTRIC DISCHARGE TUBE The invention relates to a directly heated cathode of an electric discharge tube which is activated with lanthanum hexaboride and which emits an electron beam of a small cross-section.

The known cathodes of this type consist of a rhenium wire bent in the form of a hairpin and covered cataphoretically with a layer of lanthanum hexaboride, which layer is sintered on it (Rev. Sci Inst. 8567, 1965). The drawback of such a cathode as a punctiform electron source is that the curved end of the hairpin filament is not very suitable for a good concentration of the electron beam because the surface is convex and not plane or concave. Also, a very expensive rhenium filament is required because tungsten is attacked by lanthanum hexaboride without a special intermediate layer.

It is known from Radio Engineering and Electronic Physics l2, 798-802, 1967, in particular p. 800, line 11 from bottom, to add to compressed lanthanum boride a small quantity (optimum percent by weight) of rhenium, tungsten, titanium or iridium. However, such a mixture is very difficult to compress. The said metals release lanthanum from the lanthanum boride which produces a low work function at the surface of the cathode.

It is the object of the invention to provide a cathode which is activated with lanthanum hexaboride, enables a good focusing and in addition has a long life.

According to the invention, a directly heated cathode for an electric discharge tube which is activated with lanthanum hexaboride to which a material is added which releases lanthanum consists of at least one tungsten filament on which a molybdenum plate is welded having thereon a compressed mixture of lanthanum hexaboride and rhenium or a tungsten boride, the lanthanum boride being at most percent by weight of the whole. In its simplest form the filament is a wire bent in the form of a hairpin on the top of which the molybdenum plate is welded. In cathodes of a slightly larger diameter, a wire bent in a zig-zag manner or a spirally wound wire, or separate hair-pin wires may be used as a filament.

The molybdenum plate may be compressed simultaneously with the layer of powder compressed on it or it may consist of a compact metal. Tungsten boride preferably consists of W B or W 8 No excessive formation of free lanthanum is obtained. In so far as rhenium is used, this occurs only in powder form in the compressed layer which has a smaller influence on the price than a rhenium filament. V

In contrast with the known compositions, the mixture according to the invention can be excellently compressed.

In the construction according to the invention the molybdenum forms a protective layer between the lanthanum boride and the tungsten filament. As a result of ties and long livescan be obtained with such cathodes.

Just like other lanthanum hexaboride-activated cathodes, those according to the invention are also suitable for discharge tubes having poor vacuum conditions and for tubes in which the cathodes are exposed to air several times, for example, in electron microscopes.

It is to be noted that a cathode is known from the US. Pat. No. 3,027,480 in which a mixture of tungsten, thorium tetraboride and rhenium as a mixture is sprayed on a tungsten cylinder or in an aperture in a cap. The mixture may also be shaped previously to form a hollow cylinder. The less agressive thorium tetraboride makes a protection between the mixture and the tungsten supporting body which in addition is indirectly'heated superfluous. Moreover, the mixture is not compressed which in the cathode according to the invention is necessary for a good life.

The invention will be described in greater detail with reference to the drawing which shows a cathode ac cording to the invention.

Inthe FIGURE, 1 denotes a hard glasstube bottom in which supply wires 2 and 3 of an iron-nickel-cobalt alloy are sealed. A tungsten wire 4 of 0.18 mm diameter is welded to the wires 2 and 3. Welded to the top ofthe hairpin wire 4 is a compressed cathode body consisting of a layer 5 of molybdenum powder with on top a layer 6 of a'mixture of rhenium powder and lanthanum hexaboride in a weight ratio of 5:2.

The overall thickness of the cathode body is 0.3 mm

and the diameter is 1 mm. The pressure of compression was 3,000 kg/cm Prior to compression, the molybdenum powder is fired in hydrogen at l,300 C for 30 minutes. The whole cathode body is heated in hydrogen at 1,750 C for 15 seconds. The cathode is degassed in a discharge tube at 1,600 C and activated at l,500 C. The saturation emission at 1,400 C may amount to 25 A/cm What is claimed is:

l. A directly heated cathode for an electric discharge tube comprising a tungsten filament, a molybdenum plate welded to said tungsten filament, and a layer con sisting of 30 percent by weight of a compressed mixture of lanthanum hexaboride and the remainder essentially rhenium or a tungsten boride on said molybdenum plate.

2. A cathode as claimed in claim 1, characterized in that the tungsten boride consists of W B or W 8 

1. AN ACYLATED TRIPEPTIDE OF THE FORMULA AND HAVING THEREON A COMPRESSED MIXTURE OF RHENIUM WITH CAC-PHE-ALA-PRO LANTHANUM HEXABORDIDE. INSTEAD OF RHENIUM, A TUNGSTEN BORIDE WHEREIN CAC IS CHLOROACETIC ACID; SUCH AS W2B OR W2B5 MAY BE CHOSEN.
 2. A TETRAPEPTIDE OF THE FORMULA PGLU-TRP-ALA-PRO OR PGLU-LYS-TRP-ALA-PRO
 2. A cathode as claimed in claim 1, characterized in that the tungsten boride consists of W2B or W2B5.
 3. AN ACYLATED TETRAPEPTIDE OF THE FORMULA DAC-FLY-PHE-ALA-PRO- OR A-LYS-PHE-ALA-PRO WHEREIN DAC IS DIAZOACETIC ACID, AND A IS CHLOROACETIC ACID, CYCLOBUTYLCARBOXYLIC ACID, CYCLOPENTYLCARBOXYLIC ACID OR CYCLOHEXYLCARBOXYLIC ACID;
 4. A PENTAPEPTIDE OF THE FORMULA
 5. AN ACYLATED PENTAPEPTIDE OF THE FORMULA DAC-GLY-GLY-PHE-ALA-PRO WHEREIN DAC IS DIASOZOACETIC ACID;
 6. A HEXAPEPTIDE OF THE FORMULA PGLU-LYS-PHE-ALA-PRO-PRO; PGLU-K-TRP-PRO-ARG-PRO WHERE K IS ASN, NLE OR SER; PGLU-NLE-TRP-PRO-L-PRO WHEREIN L IS HIS OR GLY; PGLU-ASN-TRP-PRO-M-PRO WHEREIN M IS LYS OR GLY;
 7. AN OCTAPEPTIDE OF THE FORMULA PGLU-ILE-PRO-PRO-LYS-PHE-ALA-PRO;
 8. AN ACYLATED OCTAPEPTIDE OF THE FORMULA N-O-PRO-ARG-PRO-GLN-ILE-PRO-PRO WHEREIN N IS CYCLOBUTYLCARBOXYLIC ACID, CYCLOPENTYLCARBOXYLIC ACID IS OR CYCLOHEXYLCARBOXYLIC ACID AND O IS TRP, TYR,
 9. A NONAPEPTIDE OF THE FORMULA PGLUC-TRP-PRO---P-P-RO-Q-IIE-PRO-PRO WHEREIN P IS ARG, ARG, HIS, LYS OR GLY AND GLN OR ASN; PGLU-TRP-PRO-R-PR-S-T-ALA-PRO WHEREIN R IS ARG OR ORN, S IS NLW OR GLN AND T IS ILE OR PHE; PGLU-O-TRP-PRO-ORN-PRO-S-T-PRO-PRO WHEREIN S AND T ARE AS DEFINED ABOVE; PGLU-O-PRO-ARG-PRO-GLN-ILE-PRO-PRO WHEREIN O IS AS DEFINED ABOVE PGLU-TRP-PRO-ARG-PRO-GLN-NLE-T-PRO-PRO WHEREIN T IS AS DEFINED ABOVE;
 10. A DECAPEPTIDE OF THE FORMULA PGLU-K-TRP-PRO-P-PRO-Q-ILE-PRO-PRO; WHEREIM K, P AND Q ARE AS DEFINED ABOVE; PGLU-U-TRP-PRO-P-PRO-GLN-ILE-PRO-PRO WHEREIN U IS LYS OR GLU;
 11. AN UNDECAPEPTIDE OF THE FORMULA PGLU-TRP-PRO-ARG-PROV-V-PRO-W-ILE-PRO-PRO WHEREIN V IS THR OR GLY AND W IS GLN OR GLU;
 12. A TRIDECAPEPTIDE OF THE FORMULA PGLU-GLY-GLY-TRP-PRO-ARG-PRO-GLY-PRO-W-ILEPRO-PRO 